An ensemble effect is achieved when a musical tone sounds like it comes from more than one instrument. A note played by a group of violins sounds different than the same note played by a single violin. The ensemble effect is produced by the resulting combination of tones of nominally the same but of slightly unequal pitches of the several instruments. The ensemble effect is further enhanced by differences in the tonal quality of the different instruments. Therefore, to reproduce the "warmth" of tone associated with the ensemble effect by a tone synthesizer, it is desirable to create multiple tones which differ slightly both in pitch and in tonal quality.
The generation of tones producing an ensemble effect in electronic musical instruments is well-known. See, for example, U.S. Pat. Nos. 3,347,973; 3,429,978; 3,884,108; and 3,978,755. Each of these patents disclose methods for producing an ensemble effect by generating frequencies which are offset from the true musical frequency. This has been accomplished in such prior art patents by utilizing multiple tone generators. In copending application Ser. No. 644,450, filed Dec. 29, 1975, entitled "Ensemble and Harmonic Generation in a Polyphonic Tone Synthesizer" and filed by the same inventor as the present application, there is described an ensemble system for a polyphonic digital tone synthesizer capable of producing tones which differ in pitch as well as in tonal quality. This is accomplished by providing separate digital tone generators and requires multiple master data sets to be computed to control the waveforms generated by the several tone generators.